William J Stewart, PhD
Biologist. Educator. Artist.
Current Work
I am fascinated by how animals live and function in their environment. Fish, for example, can detect the most subtle movements of nearby water, an ability that helps them navigate dark habitats, find food, and evade predators. Fish achieve this with the lateral line system, a collection of mechanoreceptors on their skin. To better understand this system, I have teamed with Dr. Jimmy Liao to study the flow that stimulates a single receptor of the lateral line. Using techniques from biomechanics and electrophysiology, we are identifying the types of water motion that fish care about most.
Predator-prey encounters in fish
My doctoral work taught us that fish escape predators by sensing motions of water. The ability to evade predators is central to the ecology and evolution of many fish species, yet it is largely unclear how prey fish detect and evadee predators. To resolve this, I worked with Dr. Matthew McHenry (University of California, Irvine) to investigate the sensory biology and biomechanics of a prey fish (zebrafish larvae, Danio rerio) during the rapid events of a predator encounter. I used a wide variety of techniques, such as high-speed videography (Stewart et al., 2013), 3D flow quantification (Stewart et al., in review), 3D morphometrics (Stewart and McHenry, 2010), and mathematical modeling (Stewart and McHenry, 2010), to better understand predator evasion in fish. We found that flow sensing is critically important for prey fish to evade predators and that prey use their highly-sensitive lateral line system to detect the subtle flows of approaching predators.
Gecko adhesion and locomotion
My postdoctoral work has helped us better understand how geckos stick to surfaces. While adhesion in geckos has been studied for hundreds of years, it remains unclear which components of the adhesive system the animal actively controls. Do geckos control the strength or application of adhesion, or are these factors intrinsic to the system and, hence, fundamentally passive? While a postdoc in the lab of Timothy Higham at UC, Riverside, I compared the clinging strength of Tokay geckos before and after death using a novel device that measured the force of adhesion with unprecedented control. These experiments showed that death has zero effect on adhesive force, indicating that strong gecko clings are fundamentally passive.
Squid locomotion
My masters work showed us how squid swim with fins. Squid are remarkable swimmers that employ a complex lcomotive approach, involving both a pulsed jet and fins, which enables them to be fast and highly maneuverable. Despite this strong ability to swim, it is unknown how squid coordinate their multiple propulsors. Working with Dr. Ian Bartol (Old Dominion University), I used global fow quantification to reveal that the fins of squid are integral contributors to locomotion by generating more force than the pulsed jet at low speeds. We also identified four unique wake signatures produced by the fins, suggesting that the fins are highly flexible structures that adjust to the squid's specific locomotive needs.